Heat sensitive copying sheet



March 1, .1960 w. H. VANDER WEEL 2,927,039

HEAT SENSITIVE COPYING SHEET Filed March 7, 1957 BLUSH LAGOUER OPAOUEBACK/N6 SHEET TRANSLUOE/VT BACK/N6 SHEET FIG. 3

THIN FLEXIBLE HEAT RES/$774M? ORGAN/6 POLYMER/0 F /LM INVENTOR. WALTERH. \QJER WEEL v I attorney HEAT SENSITIVE COPYING ,SHEET Walter H.Vander Wee], Ontario, N.Y., assignor to Label- .on Tape (30., Inc.,Rochester, N.Y., a corporation of New York Application March 7, 1957,Serial No. 644,541 Claims. (21. 117--36) This invention relates tocopying sheets which may be utilized to make copies of original graphicmaterial such as typewritten sheets, printed pages, photographs and thelike by exposing to heat the original graphic material together with acopying sheet.

It has been proposed heretofore to provide copying sheets from whichcopies of such original material may 'be made by placing the copyingsheet against the sheet or body of original material to be copied andexposing to radiant heat energy the two sheets thus placed injuxtaposition.

Furthermore a variety of compositions have been proposed for applicationto paper to provide such copying :sheets and also to providetemperature-sensitive sheets *of other types such as sheets forrecording data in instruments of various sorts.

Such copying sheets to be of greatest value should *meet a large numberof requirements. They should have wide latitude, that is, at a giventemperature the image in the copying sheet should be formed quickly andyet it is desirable that it be possible to cause the image to be formedin said copying sheet by exposure at any temperature Within a fairlywide temperature range. It is desirable that they have a high speed. Asheet having a low speed must be exposed for a long time in order tocause image formation, and a sheet having a narrow latitude must beexposed at precisely the correct temperature in order to provide for theformation of an image consisting of a suitable copy of the material tobe copied. If a sheet having such narrow latitude be exposed at a highertemperature it will change color throughout its entire area no matterhow quickly nor how "long exposed rather than forming a copy of thematerial to be copied whereas if exposed at a temperature below those atwhich a reaction is induced it will not form a copy at all.

Such sheets should also have high temperature storage stability, thatis, they should not deteriorate under conditions under whichmost paperand oifice materials are used and stored in business, industry andcommerce. Storage rooms and officcs often contain storage cabinetslocated above or adjacent to heating units such as radiators and thelike and temperatures in such storage cabinets not unusually reachtemperatures of from 140 to 160 F. Duration of storage in such placesmay be from only a few days to as much as one to two years or more. Itis also of importance that the copying paper not have a surface whichwill stick or adhere or ofiset, i.e., transfer, in any fashion to thesurface of the original material being copied. The surface also shouldbe one which will prevent blocking, i.e., partial adherence betweensheets of copying paper stacked .on top of vone another. In order toavoid such adherence or offsetting -.or blocking it is necessary thatthe surface not be greasy orwaxy or tacky. Itshould not begreasyinthemanner .exhibited by wax-impregnated paper normally referred to aswax paper and represented by Wax coatings applied ower paper stock orby-rcarbon paper? which comprises United States Patent a thin paper stockhaving a coating of wax thereon with carbon black or other pigmentmaterial dispersed in the wax. A tacky surface is represented in anoutstanding instance in a particularly objectionable manner for thispresent purpose by the surface of pressure sensitive tapes wherein arubber base adhesive is applied to a base sheet such as cellophane orpaper.

It is also extremely desirable that .suitable'thermalcopying paper beinsensitive to pressure from sharp instruments of the sort it is likelyto undergo in handling; it should be insensitive to the pressure ofstyli, pencils, finger nails, corners of typewriters, staplers and otheroflice equipment'whic'h maybe sharplybroug'ht in contact with it.

Suitable copying sheets should also be relatively easily filea'ble,i.e., not too flimsy to be placed easily into "file folders and shouldnot have a tendency to curl since curling also makes handling and filingof the sheets more difiicult. It is also necessary and desirable thatthe copying sheet be stable to light; or in other words, to "radiationfrom the electro-magnetic spectrum in the visible range.

In accordance with my invention I provide a thermalcopying sheet havingimproved high temperaturestorability, higher speed and wider latitudeand greater resistance to blocking and offsetting or adhesion tomaterial to be copied than sheets heretofore proposed. In accordancewith a preferred embodiment of-myinvention I provide a sheet of whitepaper, more or less opaque to light, about .015 inch thick with a firstcoating of a waxy or other fusible material melting between 1'65 F. and210 and over this second coating I provide a non-waxy, non-tacky layerof non-stylus pressure sensitive iblus'h coating which has athermal-sensitivity above 2 15* "R, i.e., which melts above'2l5 F. andis adapted to lac-transparentized or at .least translucentizedthroughout suitable areas corresponding to material to be copied bycausing areas of said first coating adjacent thereto to become a liquid;the second layer does not itself become melted .or softened.

There have been heretofore proposed a number of formulations forcoatings on paper to provide thermalcopying paper wherein sensitivity tothermal-radiation is obtained by providing in said formulation tworeactants which are of light color or disposed in a light .colored mediaand which react upon being exposed to a suitable temperature to providea dark colored reaction product. Usually one of such reactants has beena metal salt, often a salt of a heavy metal, and in :some cases botho'f:said

reactants have been salts of heavy metals. With such formulations it hasbeen "generally necessary that one of the reactants, or both of thereactants or one of :the reactants and the media in which the reactantsare dis persed, melt within a range to which the material is :to besensitive and :such sheets have exhibited a narrower latitude and lowerspeed than desirable and have been particularly deficient in being.storable for only very short periods at high temperatures. Thus onesample of .a thermal-copying paper utilizing .a ,metal :salt in thesensitive layer thereof and believed to .contain :in said :sensitivelayer an iron salt such as ferric rmyristate .or ferric .stearate and acompound such as tannic acid or .hexamethylenetetrarnine-gallic acidreaction product, turned cloudy gray when stored for six hours at 140 F.and were unusable. Likewise storage 10f such papers at F. for four days.or at "F. ;fo,r'2 days .cause them to be unusable.

Another disadvantage exhibited by previous heatsensitive copying papershas been poor contrast due to the color of reactants and reactionproducts utilized which limits the colorwhich-may be used .to these provided by such reactants and products; for ex mple, ithe provided toexhibit any desired color contrast, there being no limitation imposed byreason of being limited to certain combinations of reactive chemicals.

' Certain patents have heretofore proposed providing a blush lacquercoating on paper backing sheets. United States Patent 2,591,660 providesa blush coating on a backing sheet which is described as sensitive to atemperature of 80 and Patent 2,299,991 also describes such a coating ona dark surfaced foundation, the coating of the latter patent however,being sensitive to pressure such as may be exerted by a cold stylus orother extraneous influences such as finger nails, paper clips and thelike, a particularly objectionable feature for thermal-copying paper. Inthe latter patent the backing sheet is dark paper or paper which isdarkened by coating with a hardened dark colored coating. In otherwords, each of these patents provides a dark foundation backing sheetcovered with a single blush lacquer layer. The material described inPatent 2,299,991 is not suitable as a thermalcopying paper because ofits pressure sensitiveness while the material described in Patent2,591,660 has less than desirable latitude, contrast and speed and failsto have other desirable qualities as herein set forth to an extentsufiicient to make it relatively ineffective as a suitable copyingpaper. Because the blush lacquer layer is directly receptive to indiciaproducing media in both of these sheets, there exists a tendency tooffset or transfer material of the coating to adjacent surfaces. This isespecially true, moreover, of sheets having a waxy layer of materialpresent and providing one surface of a sheet, as for example in carbonpaper, wherein copies are made by utilizing such offsetting ortransferring tendency.

With the copying sheet according to my invention, there is no offsettingor transfer of any of the material of the copying sheet onto the sheetof material being copied because no waxy surface is present at anoutside surface of the copying sheet, the waxy or other fusible materialbeing entirely covered by the blush coat and the blush coat itself beingneither waxy nor greasy and not having been melted or softened as aresult of the application of the heat. In the copying sheet of myinvention the heat which produces the image in the copying sheet causesmelting only of the layer of fusible material and this layer does notcause melting of the material of the blush or top coat.

It is thus an object of my invention to provide an improvedheat-sensitive copying sheet which is not sensitive to stylus pressure,which is non-sticky and nonblocking, i.e., has a non-tacky surfacedevoid of greasiness and waxiness and which has improved latitude, speedand contrast by reason of comprising a backing sheet provided with afirst coating which is waxy, i.e., fusible in nature and a secondcoating which consists essentially of a blush lacquer.

Further objects will become apparent from the drawings and the followingdetailed description in which it is my intention to illustrate theapplicability of the inven tion without limiting its scope to less thanthat of all those equivalents which will be apparent to one skilled inthe art. In the figures like reference numerals refer to like parts and:

Figure 1 is a magnified perspective view of a portion of a copying sheetadapted for printing by transmission of infrared rays passing throughthe sheet of material to "be copied onto the coatings of the copyingsheet:

Figure 2 is a magnified perspective view of a portion of a copying sheetadapted for reflex printing by passage of infrared rays downward throughthe translucent or transparent backing sheet, thence against the surfaceof material to be copied and thence by re-radiation or conduction intothe coatings on the copying sheet;

Figure 3 is a magnified perspective view of a portion of a copying sheetadapted for reflex printing by passage of infrared rays downward throughthe coatings at the top of the copying sheet, thence through thetranslucent or transparent backing sheet into contact with the materialto be copied and thence back therefrom upwardly by reflection,re-radiation or conduction through the translucent backing sheet intocontact with the coatings thereon;

Figure 4 is a magnified perspective view of a portion of a modified form'ofthe sheet of Figure 1;

Figure 5 is a magnified perspective view of a portion of a modified formof the sheet of Figure 2; and

Figure 6 is a magnified perspective viewof a portion of a modified formof the sheet of Figure 3.

As shown in the figures, a backing sheet which may be opaque, as shownin Figures 1 and 4, or translucent or transparent, as shown in Figures2, 3, 5 and 6, is provided with a first coating of fusible material andon top of the first coating of fusible material, with a second coatingconsisting essentially of a blush lacquer. Copying sheets made withtranslucent backing sheets may be utilized for reflex copying whereas ifthe backing sheet is opaque, copying is by the transmission method.

As shown in Figures 4, 5 and 6 the sheets of Figures 1, 2 and 3 may bemodified by applying over said second coating a layer of thin flexibleheat resistant organic polymeric film. The film may be formed apart fromthe sheet and applied by laminating or may be formed in situ by coatingor dipping. The base material is preferably one which has sufficientrigidity to provide for suitable fileability; that is, it should providea copying sheet which will not curl or be flimsy and which therefore canbe easily placed in files and the like.

Materials heretofore proposed have generally been flimsy and havegenerally curled badly so that filing of them has been diflicult. Apreferred base material is an opaque material which is reasonablytransparent to heat, has a rough surface to provide good adhesion tocoatings and has excellent uniformity of fiber structure and is devoidof fiber and filler irregularities which tend to cause graininess in animage. Suitable papers include a .019", 13 lb. (per 500 sheets of 20 x30 inch size) milo paper produced by S. D. Warren Company, Portland,Maine; a .020", 15 lb. (per 500 sheets of 20 x 30 inch size) white milopaper produced by the same company; and a .015", 25 lb. (500 sheets of24 inch x 36 inch size) white grease-proof paper made by the RiegelPaper Company. Observations of these and other papers were made with anAnsco-Macbeth densitometer to determine transparency to infrared raysand these were found highly satisfactory for this purpose. Other opaqueand transparent papers may be used and there may also be used plasticsheet materials such as cellulose acetate, cellophane, Mylar, celluloseacetate butyrate, or sheets of thermo-setting resin reinforced withglass fibers as set forth in US. Patent 2,718,476. For certain purposes,such as utilization in the aircraft industry for outlining templates tobe cut from sheets of metal, the coatings as hereinafter described maybe provided on a base sheet consisting of steel or aluminum or othermetal and for utilization for copies having high dimensional stabilityin connection with various applications in the cartographic and graphicarts industries, the coatings may be applied on a base materialcomprising tracing paper which'normally consists of a cotton or linenwoven fabric impregnated with calendered starch or other thermoplasticmaterial.

The color of said backing material is preferably light nuances to.provide improved contrast but under circumstances as. hereinafterdescribed wherein the first fusible coating placed thereon is maderelatively transparent, an opaque paper may be provided in a colorsufficiently dark. to contrast with the light color of the second layerhereinafter described.

Generally speaking a backing sheet paper which provides a particularlysatisfactory copying sheet in accordance with the invention is from.012" to .030" thick.

There is applied to the backing material, as hereinbefore described, afirst coating of fusible material which may comprise, for example, amixture of a hard wax having a high melting point with a softer waxhaving a somewhat lower melting point and coloring matter such as one ormore dyes to provide the desirable dark color therein. Carnauba wax,which melts at 170 F. to 200 F. is particularly'suitable as a wax of thefirst type and montan or ceresin or parafiin wax may be suitablyutilized as said second wax. The layer of fusible material may be clear,i.e., transparent or translucent, or it may be colored by addition ofcoloring material or use of colored Waxy materials or both. As a'coloring agent or coloring material to be included with the waxes theremay be used a pigment or a dye; a pigment, however, tends to absorbinfrared radiation with resultant heating and therefore reduces contrastand dyes are generally preferred since they tend to transmit infraredrays rather than absorbing and converting such rays into sensible heat.Suitable dyes which may be utilized include, for example, for a greencolor, a mixture of Iosol Yellow (National Aniline Company) plus 90% ofVictoria Blue, BOC, as sold by DuPont, or Victoria Blue base, as sold byDu Pont. There may also be used Crystal Violet, as sold by DyeSpecialties, Jersey City, or Methyl Violet, as sold by National AnilineCompany. To provide a dark red color there may be suitably usedRhodamine B-base as sold by Du Pont.

Preferred colors are dark green and dark blue but it is preferred toprovide for a plurality of colors so that various colors may be used forvarious purposes by ultimate users to indicate, for example, the typesof material which have been copied or locations in which such copiesshould be filed or other information.

A suitable green color can be obtained by utilizing as a component in awax formulation for the fusible layer, a ceresin wax which is yellow.There may be used, for example, ceresin #C-500 sold by Strahl, & Pitsch,or any other suitable ceresin. Ceresin wax generally melts in the range130 to 175 F.

As mentioned above, it is preferred to utilize both a hard high meltingpoint wax and a soft low melting point wax in the formulation and it isgenerally preferred to use ratios of these two waxes of from about 2 to1 to 9 to 1. With concentrations of soft wax higher than represented bya proportion of 2 to 1, the dye or. dyes which tend to be solubleprimarily in the harderwaxes tend to be precipitated out and hightemperature storage sta-:

bility is reduced; with a proportion of over about 9 to 1 of hard wax tosoft wax the layer is too brittle andtends to flake and break away fromthe base material and the top, coating. The preferred range is from 5.to 1 to 3 to 1.

As mentioned hereinbefore, either carnauba, for example, triple refinedNo. 3. North Country wax or montan wax may be used. As a soft wax theremaybe used any one of a wide number ofparaflins in placeofceresin aspreviously described.

There may also be provided in a formulation of waxes forthe layer offusible material a small quantity of oil forthe purpose of reducing oreliminating any tendency to flake and in order to make thelayer darkerfor higher contrast and to aidin assuring completesolution of the dye inthelayer. With less than about 5 no useful results are obtained andgenerally. about 1% is-theminimm with. which suitable improvement canbeobtained.

by addingoil; the preferred amount of oil is about two percent and ifmore than four or five percent be used, the oil tends to bleed or exudefrom the layer into the top or second layer of blush coating withdeleterious results. In the event that too much. oil is used, this tendsto happen particularly at higher temperatures and reduces storagestability at such temperatures. Suitable oils include castor oil,stearic acid or any long chain fatty acid, red oil and petrolatum.

The formulation for the wax is heated to from about 200 F. to about 230F. and coated on a suitable backing sheet by any suitable means; forexample, in the case of materials for templates wherein the coating isto be applied to aluminum or steel sheets, it may be applied witha brushor by spraying or dipping. Preferably it is applied by means of asuitable coating technique for. obtaining a thin coating of relativelyuniform thickness using standard coating equipment such as :a knifecoater, reverse roll coater, or the like. It is particularly suitable tocoat with a transfer roll which operates with one side of the rolldipping into a pan of the material to be coated and the other side ofthe roll running against a web of paper or other sheet material. Afterpassing over the roll the web is then passed over a Mayer equalizer rodconsisting of a rod of about one quarter inch diameter wound with wirein the form of a tight coil or helix, the wire being preferably No. 6wire.' It is preferred to coat from about 3 to 7 /2 pounds of waxy orother fusible material per ream of 500 sheets of paper each sheet being20 inches by 30 inches in size, which is equivalent to a coating of 3-to 7 /2 pounds per 283 square feet or 31 /2 square yards and optimumresults are generally obtained with about 5 pounds per ream, althoughsuitable results may be obtained with a coating as thin as .0005 or asthick as .010".

In place of the wax formulations as hereinbefore described there may beutilized a synthetic resin or synthetic resins of suitable melting pointand adhesive characteristics; for example, modified rosin esters such asStaybelites made by Hercules Chemical Company or polyterpenes such asPiccolites made by Pennsylvania Industrial Chemical Company may be usedor polyethylene glycols such as the Carbowaxes made by Carbide andCarbon Chemical Company or polyethylenes such as made by US. IndustrialChemicals Company or made by Allied Chemical and Dye Corporation orothers may be used.

However, a preferred synthetic resin for the waxy or fusible layer is alatex or latex-like composition, i.e. an emulsion comprising anelastomeric or other polymeric synthetic resin which is thermoplastic innature. Such a polymeric resin may be polyvinyl chloride,polyvinylalcohol, polyethylene, polyvinyl. acetate, copolymer of vinylacetate and vinyl chloride, halogenated polyethylene, natural rubberize. polyisoprene, polychloroprene, polybutadiene, copolymer of any oneof the last three with styrene and/ or acrylonitrile, or other monomeradapted to undergo polymerization through ethylenic unsaturation. Asuitable plasticizer may be included. A particularly suitable suchpolymeric composition has been found to be a rubber latex adhesive suchas those sold commercially. by Industrial Latex Corporation as RX 70 andRX 69. In order to make certain that a fusible layer comprising suchcomposition does not exhibit pressure-sensitiveness which isobjectionable as hereinbefore mentioned it is necessary that thethickness of such coating be maintained within the limits hereinbeforementioned.

Rather than merely a layer of such polymeric resin I may suitablyutilize a layer of material of relatively high melting point havingdispersed therethrough a very large number of very small discretefusible particles, crystal.- line or amorphous, rough and irregular orspheroidal, immiscible inthe carrier. Thus I may provide a layer ofcellulose acetate having dispersed therethrough small particles of oneor more substances such as stearic acid, potassium stearate,triphenylphosphate, N-ethyl oand ptoluenesulfonamide, N-ethylp-toluenesulfonamide, oand p-toluene ethylsulfonamide, and N-cyclohexylptoluenesulfonamide (sold commercially by Monsanto Chemical Company asSanticizer 9, 3, 8, and 1-H, respectively), camphor and solid animalfat. Other suitable carrier materials include cellulose nitrate,cellulose propionate, ethyl cellulose, ethyl acrylate, and the like.

Particular advantages of the copying sheet according to my invention arethat by reason of providing the first coat of fusible material and thesecond coat of blush coating material, the fusible material stayscompletely unchanged during storage resulting in high temperaturestorability for long periods. When a portion of the material is heated,for example, by being exposed to infrared rays while the copying sheetis in contact with the sheet of material to be copied so that portionsof it are adjacent to black letters or symbols or other graphic materialon the sheet to be copied, infrared rays are absorbed by such blackindicia with the result that adjacent portions of the copying sheet areheated more than those portions of the copying sheet which are adjacentwhite portions of the sheet of material to be copied. The fusiblematerial becomes melted adjacent to the black or dark indicia on thesheet of material to be copied and in such areas the fusible materialtransparentizes or translucentizes the blush coating by (it is believed)flowing into the pores thereof, i.e., the second coating is madetransmissive to light to the extent of transmitting at least 50% ofincident light rays in the visual range. In any event, upon removal ofthe heat source the fusible material sets again and stays setpermanently. A copy of the original material to be copied is thusproduced in the copying sheet by reason of the contrast between thetranslucentized or transparentized areas of the blush coat through whichthere is observable the dark colored fusible layer and those areas ofthe blush coat which have not been made transmissive and thereforeremain opaque and light in color.

As hereinbefore mentioned, the layer of fusible material may be clear,i.e., all dye or other coloring matter may be omitted therefrom and theunderlying base material may be made black or dark in color whereby whena portion of the sheet is heated after being coated with both the firstand second coatings, the first coat trans lucentizes or transparentizesthe second coat in the heated area thus causing the color of the backingmaterial to be observable in contrast to the unchanged portion of thetop or blush coat.

As a suitable formulation for the top or blush coating there may beutilized a lacquer made by dissolving scrap cellulose acetate in acetoneand then adding acetone and water as blushing agents, in the proportionsof about 10 parts of cellulose acetate dissolved in a solvent mixturecomprised of about 90 parts of acetone and 10 parts of water or theremay be suitably utilized pyroxylin dissolved in a solvent mixture whichcomprises water as set forth in Patent 1,449,157. Formulations utilizingethyl cellulose or cellulose acetate dissolved in mixtures comprisingacetone and water as set forth in Patent 2,519,660 may also be utilized.

If desired, a pigment or dye or other coloring matter may beincorporated as a tinting agent in the blush coat.

In order to improve the adhesion of the second coat for the first coatthere may be added to the formulation for either of the coats from 1% t03% of a relatively tacky material such as Flexowax or a modified rosinester or rosin, the material preferably being added to the formulationfor the first or fusible layer in order to avoid the presence of suchmaterial at the surface of the blush coating with possibility ofresultant transfer or offsetting.

There may also be included in either the formulation for the firstcoating or the formulation for the second coating a so called mattingagent for promoting adhesion. If added to the formulation for the top orblush coating such a matting agent may have the additional advantage ofproviding a more writable surface, i.e., a. surface more receptive topen and pencil. Such matting agents, include finely divided mineralproducts such as celite, bentonite, talc, diatomaceous earths and thelike.

Another manner by which improved adhesion between the two layers may beobtained is to heat the top surface of the layer of fusible materialjust prior to applying the formulation of the blush coating so that atthe time the blush coating is applied thereto the surface of the wax orother fusible material is soft or somewhat liquid.

it is generally desirable that the outer surface of the copying sheetaccording to the invention be receptive to pencil lead, ballpoint inkand fiuid ink in order that corrections, interlineations or the like maybe easily made thereon.

For this purpose I may add a matting agent as mentioned above or may addinstead or additionally a finely divided solid which is insoluble in theblush coating carriers, i.e., insoluble in the solvent system utilizedfor dissolving the resin of the blush coating formulation. Such a finelydivided solid may be colored to provide a colored or tinted blush coatas hereinbefore mentioned but is generally preferably light colored orwhite and may improve adhesion of the blush coat to the underlyingsurface of the first coating. Utilization of such a finely divided solidhas been found to provide an improved White or light color in the blushcoat and has been found to increase the temperature resistance of theblush coat thereby increasing the high temperature storability andreducing the tendency of the blush coat to be melted or transparentizedby application of heat thereto or to be translucentized ortransparentized other than by melting of the underlying layer of fusiblematerial. A preferred solid for this purpose is raw starch, for examplerice starch, but there may be used other siliceous powder particles,ground earths, and the like it being necessary primarily that suchmaterial be finely divided and be absorbent with respect to the solventand resinous components in the blush coating lacquer but be insoluble inthe carriers for the blush coating, i.e., the solvent or the resinouscomponents thereof and be light. in color.

The second or blush coat may be applied by any suitable coating method;for example, it may be ap plied to stainless steel or aluminum sheets byspraying or brushing or dipping or to paper or plastic sheets in thesame manner but it is preferred generally to apply it by means ofstandard coating techniques and standard coating equipment, i.e., byknife coating, reverse roller coating and the like. A preferred coatingis obtained if the formulation is applied toa continuously advancing Webof paper by means of a transfer roll and a Mayer equalizer rod in suchquantity and at such a rate as to provide a coating having a thicknessof .0002" to .008" and optimum results have been achieved with a coating.0005" to .006" thick. The blush coatings as thus described arenon-pressure sensitive, that is are not sensitive to stylus pressure anddo not mark or exhibit any indicia when scratched with a fingernail orwith a sharp point as with a toothpick or stylus and they have nongreasyand non-waxy surfaces which are devoid of tackiness both during storageand during the time when heat is applied thereto to cause the underlyinglayer of fusible material to be melted in order to make the blush coattransmissive to visible radiation.

The invention is further illustrated by the following examples whichillustrate certain embodiments but 'are not to be taken as limiting theinvention only to those particular embodiments illustrated, it beingunderstood that otheriernbodiinents and equivalents will be apparent tothose skilled in theart.

Example 1 A coating having the following formula:

24 pounds carnauba wait 12 pounds ceresin wax 1 pound dry blue base wasmixed and coated on a web of 16 pound white milo.

paper as hereinbefore described to provide a coating of six pounds perream of fusible waxy material, green in color and about .003" thick. Asecond formulation was -prepared as follows, in accordance with Example1 of US. Patent 2,519,660:

2 Pounds. Ethyle cellulose N-IOO -5 Acetone V 45 Di-Z-ethyl hexylphthalate .75 50% solution of acetonein water 100 described. 'Excellentcopies of the printed material were .obtained. The blush coating isdescribed by James in said .patent .as softening sufficiently to providemarking with a stylus at 115 C. The presence of the starch itends to.raise its melting point so that the value of 115 is 110w. It will benoted that this is well above the temperature .atwhich I desire to printthe sheets or at ,which the sheets were printed by exposing at 180 F.

.The top coating is translucentized and transparentized reasonof themelt-ingot the first coating, i.e., the

underlying layer .of waxy material while the top blush ,eoating itselfremains unrnelted. Copying sheets were stored for one week at 150 F. andno deterioration was .pbserved. Both surfaces of the copying sheetsprepared were free ,of .taekiness and were neither waxy nor greasy anddid not off-set against the printed sheet of the material being copiedduring printing.

Example 2 sheet of cellulose acetate .015" thick is coated with Example"3 The following formulation:

24 pounds carnauba wax .6 pounds paraffin 1 pound dry blue base wasmixed and coated with a transfer roll and a Mayer equalizer rodon a webof 25-pound white grease-proof .paper as hereinbefore described.

There is then applied a coatingof the following formulation:

grams pyroxylin 100 cc. solvent mixture comprising 25% by volume ofethyl acetate and 100%. by volume of a mixture of 90% ethyl alcoholand10% water The coating is applied to the web over the first coating witha Mayer equalizer rod and corresponds to the blush .coating described inPatent 1,449,157 with theexception that the plasticizer is omittedinorder to provide'a blush- V 1 0 coating which is non-stylus pressuresensitive and which has amelting point substantially above the meltingpoint of the underlying fusible waxy layer. Copying sheets were cut fromthe resulting web and printed at 185 F. and tested for storage asdescribed in Example 1 and were found to have the desired propertiesheretofore described.

Example 4 2 pounds dry blue base dissolved in 2 pounds ,of casto oil isapplied to sheets of 25 pound mimeograph bond whieh is relativelytransparent to infrared radiation by spreading the formulation, mixedand heated to 210 F., over the sheet with a rod to provide a coatinghaving the thickness of from .0005"to .006. Over said first coatingthere then was applied at room temperature with a rod a second coating.001" to .004 thick ofthe following formulation:

15 pounds cellulose acetate .60 pounds acetone having added thereto amixture of 25 pounds acetone and 30 pounds water Sheets thus preparedwere printed as in Example 1 and found to have the goodproperties-therein described. The 'top coating formulation thus appliedis described in Patent 2,519,660 as marking at 170 C. In any event, itwas found that the compositionremained solid and provided the desirablesurface properties of nontackiness and being neither waxy nor greasyduring printing, not off-setting on the copy sheet or other copyingsheets during storage or on the material being copied .duringprinting,the top coating remaining unmelted during printing, storing and beingtranslucentized and transparentized entirely as a result of melting ofthe underlying waxy layer.

Example 6 Using the procedure of Example 3, an emulsion of rubber inwater sold commercially by the industrial 'Latex Corporation as RX 70was applied with transfer roll and Mayer equalizer in place of the waxformulation thereinset forth and copying sheets were obtained having thesame desirable properties.

Example 7 95 parts-+- 1500 grams polyvinyl acetate beads (soldcommercially by Colton Chemical Corporation as Vinac B 3500mil. acetone'5 parts triphenyl phosphate The above materials were thoroughly mixedto provide a viscous fluid which was then coated on a .003" white opaquespecialty paper with a coating rod and dried to evaporate the solvent,to thereby provide a coating .0005" to .002 thick. A coating of theblush lacquer formulation of Example 1 was then applied thereupon anddried. Sheets thus prepared exhibit good hightemperature storability andsuitability for thermal print- Any one of the several sheets prepared inaccordance *withtheforegoing examples may be provided over "theaforedescribed top or blush coating with a layer of a transparent thinfiexible heat resistant organic polymeric resin which may comprise, forexample polymethyl methacrylate or may comprise cellulose acetate orregenerated cellulose or the like, generally a thermoplastic organicsynthetic polymeric resin being preferred in a thickness of from .0002"to .002", to provide greater rigidity in the sheet, to reduce tendencyto curl, to improve storageability and to provide a sheet having aglossy appearance. Said overlying layer may be a film and may be appliedby laminating or may be applied by coating thereon a lacquer formulationcomprising the desired resinous component or components. Such lacquerformulation may comprise the desired resinous component such aspolymethyl methacrylate, polyethyl methacrylate, cellulose acetate,cellulose acetate butyrate, or the like dissolved in suitable solvents,the material being applied by any standard coating technique for thispurpose such as spraying, dipping or brushing or preferably coating witha roller, knife, or Mayer equalizer rod or the like. It is desirablethat-the outer surface of such layer be receptive to pen and pencil andsuch receptivity to be provided by abrading with said paper or sandblast or the like, or by etching with a solvent or mixture of solventsor by calendering with a suitably embossed roll.

A particularly desirable attribute of copying sheets produced inaccordance with my invention is that a copying sheet according to theinvention which has been printed from original material, i.e., on whichthere has been printed an image by exposing the sheet to infraredradiation while in contact with material to be copied, may thereafter beused as an original from which another copy can be made on anothercopying sheet according to the invention. This has not been possiblewith thermal copying sheets hereinbefore. The sensitivity and thelatitude, etc. of the sheets of my invention is such that the backgroundin the copying sheet may not be blackened by infrared rediation whenexposed for a short time together with another such copying sheet uponwhich an image has already been made and at the same time 'thoseportions of the second copying sheet in contact with previously exposedand printed portions of the first copying sheet print to form an imagecorresponding to the image on the first copying sheet.

Printing may be accomplished in any suitable manner; a preferred manneris to utilize a machine or any suitable device for exposing to a heatsource the copying sheet while in contact with a sheet of originalmaterial to be copied such as a printed page or a sheet of paper havingtypewritten indicia thereon to a heat source. Suitable means isdescribed in such patents as US. Patents 2,663,655 and 2,740,895 forreflecting infrared radiations from a highly heated rod or filamentagainst a portion of both the copying sheet and the sheet of material tobe copied while the sheets are passed over the rod or filament, beingheld in place between a belt of heat resistant synthetic resin, such as,for example polychlorotrifluoroethylene, and suitable holding means.

The copying sheets of the invention may not only be utilized for copyingsuch conventional graphic material as printed or typewritten sheets butmay be used to copy other graphic material such as photographic printsand negatives and hand-written or drawn sheets and nongraphic materialssuch as apertured and non-apertured masks or stencils carrying visuallyunobservable indicia or apertured indicia.

In addition to the base material provided with a first layer of fusiblematerial and a second or blush coat layer and, in some instances, athird layer of transparent organic synthetic resin, there may beprovided on the opposite side of the base material from the aforesaidcoatings, a coating of either waxy or other fusible material or lacquersuch as a coating of raw or bleached montan wax or cellulose acetate 01py oxylin or the like in order to improve the properties of the sheet bymaking it more rigid and less likely to curl when exposed to excessivelylow or excessively high temperatures or humidities, etc. Such coatingmay in some instances have ,a somewhat deleterious effect on otherdesirable properties of the sheet but a coating is generally preferredwhich will not thus afiect other properties of the copying sheet such aslatitude, contrast, speed and resistance to blocking, oil-setting andthe like.

In some instances it is desirable to provide indicia on the copyingsheet while in web form prior to cutting it into smaller sheets or onthe smaller. sheets after they are cut from the web for any one of amultitude of purposes: for example, advertising material, trademarks,indication of type or grade, product identification and the like may bedesirably provided on the sheet. Such indicia may be provided by rollinga heated wheel or otherwise passing a marking tool along one or moreedges of the web or small sheets cut from the web or coatedindividually, the-wheel being provided with upraised or indentedportions corresponding to the indicia to which it is desired to provideon the sheet to thereby heat these portions of the sheet contacted bythe marking tool and cause indicia to appear thereat. Such indiciaalternatively or additionally, if desired, may be provided by printingthereupon using standard printing inks and technique.

In some instances, it may be desired to provide copying sheets adaptedfor certain highly specialized uses wherein it is desired to make copiesof not all but only a portion of the indicia appearing upon an originalsheet. For example, it is a well known procedure in many businesses toprepare shipping lists or packing lists by making a copy of that portionof the indicia appearing upon the original invoice which relates only topacking or shipping. Normally the indicia which appear on the invoiceand which it is desired to omit on the packing list are the prices andpricing information. For utilization in this manner, copying sheets canbe prepared according to my invention wherein the first and secondcoating and, if desired, the third layer, are provided only in thoseareas of the coating sheet in which it is desired to make a copy of theindicia which appear upon certain original sheets.

It may be seen from the examples and description given herein that myinvention is broad in scope and is to be limited only by the claims.

Having thus disclosed my invention, I claim:

1. A heat sensitive dry non-light sensitive copying sheet devoid ofsensitivity to stylus-pressure and having surfaces devoid of tackinessand waxiness for making visible legible copies in contrasting tonesdirectly from material to be copied by exposure to infrared rayscomprising a sheet of backing material having thereon a first coating.0005" to .010" thick consisting essentially of a heat-sensitive fusiblematerial WhlCh is solid and nontacky below about F. and melts to aviscous liquid at from 165 F. to 210 F. the combination of said backingsheet and said first coating being dark colored to contrast with a lightcolored second coating and having on said first coating a second coatingof a non-stylus-pressuresensitive blushed light-colored lacquer filmdevoid of tackiness which is normally opaque below a temperature ofabout 215 F. but which is adapted to be made at least translucent bymelting of said first coating and to remain at least translucent uponsubsequent solidification of said first coating and which has anon-greasy and nonwaxy surface before, during and after being madetranslucent. v

2. The copying sheet of claim 1 wherein said backing material is lightcolored substantially opaque paper .012" to .030" thick and relativelytransparent to infrared rays and said first layer is of a colorsufilciently dark to contrast with the light color of said second layer.

3. The copying sheet of claim 1 wherein said backing material issubstantially opaque paper of a color sulfi- 13 ciently dark to contrastwith the light color of said sec ond layer, .012 to .030 thick andrelatively transparent to infrared rays and said first layer issubstantially transparent.

4. The copying sheet of claim 1 wherein said backing material issubstantially transparent organic polymeric material.

5. A copying sheet in accordance with claim 1 having on said secondlayer a thin flexible heat resistant organic polymeric film. I

6. A heat sensitive dry non-light sensitive copying sheet devoid ofsensitivity to stylus-pressure and having surfaces devoid of tackinessand waxiness for making visible legible copies in contrasting tonesdirectly from material to be copied by exposure to infrared rayscomprising a sheet of backing material having thereon a first coating.0005 to .010" thick consisting essentially of a heat-sensitive fusiblematerial which is solid and nontacky below about 165 F. and which meltsto a viscous liquid at from 165 F. to 210 F. the combination of saidbacking sheet and said first coating being dark colored to contrast witha light colored second coating and having on said first coating a secondcoating .0002" to .008 thick of a non-stylus-pressure-sensitive blushedlightcolored lacquer film devoid of tackiness which is normally opaquebelow a temperature of about 215 F. but which is adapted to be made totransmit 50% of incident light rays in the visual range by melting ofsaid first coating and to remain thus transmissive to light uponsubsequent solidification of said first coating and which 14 has anon-greasy and non-waxy surface before, during and after being made thustransmissive.

7. The copying sheet of claim 6 wherein said backing material is lightcolored substantially opaque paper .012" to .030" thick and relativelytransparent to infrared rays and said first layer is of a colorsufiiciently dark to contrast with the light color of said second layer.

8. The copying sheet of claim 6 wherein said backing material issubstantially opaque paper of a color sufliciently dark to contrast withthe light color of said second layer, .012" to .030" thick andrelatively transparent to infrared rays and said first layer issubstantially transparent.

9. The copying sheet of claim 6 wherein said backing material issubstantially transparent organic polymeric material.

10. A copying sheet in accordance with claim 6 having on said secondlayer a thin flexible heat resistant organic polymeric film. i

References Cited in the file of this patent UNITED STATES PATENTS2,299,991 Kallock Oct. 27, 1942 2,306,525 Cummings Dec. 29, 19422,519,660 James Aug. 22, 1950 2,710,263 Clark June 7, 1955 FOREIGNPATENTS 705,417 Great Britain Mar. 10, 1954

1. A HEAT SENSITIVE DRY NON-LIGHT SENSITIVE COPYING SHEET DEVOID OFSENSITIVITY TO STYLUS-PRESSURE AND HAVING SURFACES DEVOID OF TACKINESSAND WAXINESS FOR MAKING VISIBLE LEGIBLE COPIES IN CONTRASTING TONESDIRECTLY FROM MATERIAL TO BE COPIED BY EXPOSURE TO INFRARED RAYSCOMPRISING A SHEET OF BACKING MATERIAL HAVING THEREON A FIRST COATING.0005" TO .010" THICK CONSISTING ESSENTIALLY OF A HEAT-SENSITIVE FUSIBLEMATERIAL WHICH IS SOLID AND NONTACKY BELOW ABOUT 165*F. AND MELTS TO AVISCOUS LIQUID AT FROM 165*F.TO 210*F. THE COMBINATION OF SAID BACKINGSHEET AND SAID FIRST COATING BEING DARK COLORED TO CONTRAST WITH A LIGHTCOLORED SECOND COATING AND HAVING ON SAID FIRST COATING A SECOND COATINGOF A NON-STYLUS-PRESSURESENSITIVE BLUSHED LIGHT-COLORED LACQUER FILMDEVOID OF TACKINESS WHICH IS NORMALLY OPAQUE BELOW A TEMPERATURE OFABOUT 215*F. BUT WHICH IS ADAPTED TO BE MADE AT LEAST TRANSLUCENT BYMELTING OF SAID FIRST COATING AND TO REMAIN AT LEAST TRANSLUCENT UPONSUBSEQUENT SOLIDIFICATION OF SAID FIRST COATING AND WHICH HAS ANON-GREASY AND NONWAXY SURFACE BEFORE, DURING AND AFTER BEING MADETRANSLUCENT.